Robots are commonly used in industrial processing environments. In semiconductor processing, robots transport substrates such as wafers or PCB (printed circuit board) panels to and from storage locations and/or various processing stations. The highly repetitive nature of the motions involved and the speeds required for high throughput make robots ideal candidates for these tasks. FIG. 1 is a plan view of a conventional processing environment 100, in which a semiconductor wafer 108 is transported between various processing stations 110 by a robot 200. In certain embodiments, the robot is also capable of translational motion, along the direction X as shown, typically through use of a track system (not shown). Additional transport destinations, such as 112 and 114, may be for measurement or storage of the wafers 108. The environment 100 may be a closed, controlled vacuum environment, delineated by the perimeter dashed line.
Robot 200 includes a robot body 201 and a robot arm 202, and is shown in more detail in FIG. 2. Robot arm 202 exhibits angular (θ), radial (R) and Z motions in a cylindrical coordinate system. Angular motion refers to rotation of the robot arm 202 about a primary axis A at which it is pivotably coupled to the robot body 201. Radial motion is extension/retraction motion of the robot arm 202 to and from the primary axis A. Z motion is elevation of the robot arm 202 and/or body along the axis A. The motions are imparted by one or more independent or linked motors (not shown).
Robot arm 202 includes three links, although a different number of links is possible. These links 204, 206 and 208 may be dependently or independently actuatable to achieve the angular, radial and Z motions. The distalmost link 208, commonly referred to as the end effector, is tasked with engaging the workpiece for its transport and manipulation between, and sometimes within, the various stations 110, 112, and 114 mentioned above. The end effector 208 is pivotably mounted at its proximal end to the distal end of preceding link 206 for motion about axis B, referred to as yaw motion. This yaw motion of the end effector 208 is independent of the other links and their motions.
The manner in which the end effector interacts with the work piece is of crucial importance. Gripping forces, whether mechanical or vacuum, must be carefully controlled to avoid undue stress or mechanical insult, minimize contamination, or otherwise alter the characteristics of the work piece in any significant manner, while at the same time securely holding the work piece on the end effector. However, the pressures of increased miniaturization make these goals more difficult to achieve, as work pieces become smaller and thinner, and consequently, much more fragile and difficult to handle.